1. Field of the Invention
The present invention relates to compression methods and systems.
2. Description of the Related Art
Mathematical transformations are used in compression systems to represent audio data and/or picture data in a more efficient manner. A widely-used mathematical transformation is the Discrete Cosine Transform (DCT). To provide a substantially-identical representation of a 270 Mb/s CCIR (Comite Consultatif International des Radiocommunications) 601 video stream, a calculation accuracy of about 13 bits to 14 bits is required (see Robin et al., Digital Television Fundamentals, McGraw-Hill, pg. 360). Compression of the video stream may be achieved by discarding lesser significant bits or using fewer bits. Thus, the level of compression is directly tied to the number of places of accuracy maintained throughout the process of calculating the DCT.
Previous approaches to compressing a DCT representation include allocating unequal numbers of bits for the transform coefficients. The number of bits allocated to a transform coefficient may be based upon a variance of the transform coefficient. In this way, more bits are allocated to widely-varying coefficients than for lesser-varying coefficients.